Think i'd take the end off of it and go to other areas of the house and run some water to see if you can hear it passing by the pipe to make sure it was in fact some type of drain. Who knows what people do when building

You have a catastrophe in the making with that PVC piping inside the house.

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PVC piping can't be used inside the home. That should be removed and replaced with CPVC or PEX
PVC is only rated for use underground where the temperatures can remain cooler and constant. Using PVC for domestic hot water is a real NO-NO.

it could be, but the configuration is all wrong for a cleanout, especially since it does not appear to have a removable cap or plug. If it were a washing machine drain, then where are the hot and cold water supplies a WM would need.